This is the 4644th most frequent Russian word.
днём
"During the day."
The word 'днём' here refers to the time of day — the period when it's day, specifically the hours around midday.
Днём светло и солнечно.
During the day, it is bright and sunny.
In this case, 'днём' specifies the temporal context of the activity, indicating that the action takes place during daytime hours.
Мы гуляем в парке днём.
We walk in the park during the day.
Here, 'днём' highlights the time frame contrasting morning or evening, focusing on the daytime ambiance of the urban environment.